Since presenting our findings that disease-reversal could be observed in a conditional mouse model of Huntington's Disease, we have sought the key cellular events that led to this observation. Our current working hypothesis is that the elimination of accumulated protein is this key event. In the past funding period, we proposed that in order to test this hypothesis in vivo, first we had to use cell biology and biochemistry to identify the degradation pathway responsible, as well as to find a molecular regulator that would permit us to exert experimental control. As such, we have identified a selective form of macroautophagy that eliminates accumulating expanded polyglutamine proteins. Moreover, we determined that the protein Alfy was a key regulator of this pathway. For the next funding period, we propose to test our initial hypothesis by ascertaining the function of Alfy in the brain, and how altering its levels impacts reversal in our conditional model of HD. Further, we would like to broaden our findings by understanding how Alfy impacts the elimination of accumulating nuclear proteins, focusing on ataxin-1, and by determining if our working hypothesis is relevant in a true HD model which expresses the full length huntingtin protein. PUBLIC HEALTH RELEVANCE: Our goal is to determine the key neuronal events that can lead to the amelioration of polyglutamine expansion disorders such as Huntington's disease (HD). We have identified a pathway that eliminates the accumulated protein in neurons and we will test whether this can have a beneficial effect on mouse models of HD.